The yoko package

yoko views a nominal datatype as a band of constructors, each
a nominal type in its own right. Such datatypes can be disbanded via the
disband function into an anonymous sum of nominal constructors, and vice
versa via the band function. This library uses extensive type-level
programming to enrich its instant-generics foundation with capabilities
derived from the constructor-centric perspective.

For example, consider the following nominal datatype.

data Beatles = John ... | Paul ... | George ... | Ringo ...

This type can of course be understood as a sum of the individual
constructor types.

yoko's conceptual foundations start there. In particular, this allows a
constructor, say John, to be used independently of its original range type
and sibling constructors.

As a generic programming library, yoko extends intant-generics with
support for constructor-centric generic programming. The Examples/LL.hs
file distributed with the yoko source demonstrates defining a
lambda-lifting conversion between the two types Inner, which has lambdas,
and Prog, which has top-level function declarations instead.

These types are defined in separate modules, since they have constructors
with the same name. Indeed, the fact that they having matching constructors
named App is crucial for yoko's automatic conversion from Inner's App
to Term's App. As written, the generic lambda-lifter would continue to
work for any new Inner constructors (e.g. syntax for tuples or mutable
references) as long as constructors with the same names and analogous fields
were added to Term and the semantics of those constructors doesn't involve
binding. This default behavior of the lambda-lifter is specified in about ten
lines of user code.

Existing generic libraries don't use constructor names to the degree that
yoko does, and so cannot accomodate generic conversions nearly as well.